1. Field of the Invention
This invention relates to a method for correcting the intensity of each beam upon making a record by means of a picture scanning and recording system, and more specifically to a method for adjusting the intensity of each laser beam output from each optical fiber and correcting same to a standard beam intensity in a recording unit having an optical system which is constructed by connecting, with a plurality of optical fibers, a fixed optical system equipped with means to generate a plurality of laser beams and AOMs (Acousto-optic light modulators) adapted to regulate the intensities of the laser beams and a mobile optical system in which a projection lens is displaceable parallel to the axis of a recording drum so as to subscan the recording drum.
2. Description of the Prior Art
In a picture scanning and recording system for graphic arts, a reproduced picture image of an original picture is recorded on a photosensitive material such as film by photoelectrically scanning the original picture, halftone-processing the resultant signals to obtain picture signals, and then scanning the photosensitive material placed in the recording unit so as to record the picture signals on the photosensitive material.
FIG. 1 is a fragmentary schematic view showing a recording unit useful in the practice of this invention.
A laser beam 2 radiated from a laser 1 is split into a plurality of laser beams 4a-4j by means of a plurality of beam splitters 3, followed by their optical modulation by a plurality of acousto-optic light modulators (AOMs) 5a-5j.
Laser beams 6a-6j, which have been adjusted or regulated in beam intensity by the acousto-optic light modulators, are then caused by their corresponding apertured plates 7 and lenses 8 to enter incident portions 11 of a plurality of optical fibers 9a-9j respectively.
A fixed optical system 12 is constructed of the laser 1 and incident portions 11 as well as each of the members interposed therebetween.
Tip portions 13a of the optical fibers 9a-9j are, as illustrated in FIG. 2, held in a state aligned in a row by a holder 13 mounted on a movable carrier 14.
A recording drum 16, on the circumference of which a recording film 15 is applied, rotates in a direction indicated by an arrow 17. A projection lens 18 projects beams from the tip portions 13a of the fibers 9a-9j on the film 15 so that the recording of each picture is carried out.
A support 19, on which the projection lens 18 is supported, is mounted on the movable carrier 14 in such a way that the support 19 can advance and retreat in directions indicated respectively by arrows 21, 22, in other words, in the direction of a normal line of the recording drum 16. The movable carrier 14 may be reciprocated in parallel with the longitudinal axis of the recording drum 16, as indicated by an arrow. 23.
A half mirror 24 is fixedly disposed between the tip portions 13a of the optical fibers and the projection lens 18, whereby to reflect each beam, which has been reflected back from the film 15, toward an image sensor (photoelectric sensor) 25. The image sensor 25 is fixedly mounted on the movable carrier 14 at a position optically and practically equivalent to the locations of the tip portions 13a of the optical fibers relative to the half mirror 24.
The recording of each picture on the film 15 is carried out by moving an mobile optical system 26 in the direction indicated by the arrow 23 while rotating the recording drum 16.
A part of the image sensor 25 is depicted in FIG. 3. Beams, which have passed out of the fibers 9a-9j, are detected by the image sensor 25.
So long as images, produced at the tip portions 13a of the optical fibers, are projected precisely on the surface of the film 15 by the projection lens 18, images which are produced on the image sensor 25 are well-defined images having the same dimensions as the images 9a-9j actually produced at the tip portions 13a of the optical fibers, as shown by a solid circle 27a. When the images are not correctly focused on the surface of the film, poorly-defined images are produced on the image sensor 25 as indicated by dashed circles 27b.
Here, the output signals of the image sensor 25 are concentrated at a central part and give a maximum value S.sub.0 as shown in FIG. 4a when the focusing is correct. When the focusing is incorrect on the other hand, the output signals are scattered and the value of the central part is smaller than the maximum value S.sub.0, as illustrated in FIG. 4b.
In FIG. 5, all the ten optical fibers 9a-9j are lightened, and laser beams 28 which have been reflected back from the film 15 are detected by the image sensor 25. "Circles" indicated respectively by letters a-j designate optical fibers 9a-9j.
The fixed optical system 12 and mobile optical system 26 of the recording unit, both of which systems are illustrated in FIG. 1, are connected together by the optical fibers 9a-9j as mentioned above. When the tip portions 13a of the fibers and the projection lens 18, which are both contained in the mobile optical system 26, move in the direction indicated by the arrow 23, the spectrum pattern of the outputs of the fibers changes and the intensity of each beam output from the lens is thus varied, thereby raising a danger that the recording operation on the film 15 may be hampered.